1. Field of the Invention
The present invention relates to a destructuring apparatus in which wood chips are passed between closely operating rolls with compressive forces being exerted on the chips by the rolls, and relates more particularly to protecting the working surfaces of the closely operating rolls through the use of an apparatus to detect the existence of tramp material contained within the flow of wood chips, such that when tramp material is detected the closely operating rolls adjust to allow the flow of wood chips and tramp material to pass.
2. Description of the Prior Art
In a typical papermaking process, logs are debarked and chipped and the wood chips are treated to release individual cellulose fibers for the preparation of paper making stock.
One device for treating the chips to enhance liquor penetration and subsequent pulping operations is a wood chip cracking apparatus disclosed in U.S. Pat. No. 4,953,795, wherein chips are passed between closely operating rolls with compressive forces being exerted on the chips by the rolls. Another form of chip processing device is a chip slicer which includes a rotor operating within a drum, wherein oversized chips are forced against knives and sliced to acceptable thickness.
Common to chip processing devices is a conduit for handling the chips being led to the chip processing device and for controlling a uniform supply of wood chips to the chip processing device. Also common to all chip processing devices is the risk that tramp material, e.g., metal, stones, dirt, debris, etc., is contained within the chip flow stream, and such tramp material has a devastating effect on the chip processing apparatus, breaking knives or damaging operating surfaces to the extent that the machine must immediately be shut down, and the resultant damage repaired and/or equipment replaced.
A device for preventing damage to destructuring apparatuses due to the presence of tramp material is disclosed in U.S. Pat. No. 5,263,651, wherein an apparatus is provided capable of handling a continual flow of wood chips to a chip processing machine and automatically bypassing or shunting tramp material without interrupting the continuous machine operation and automatically restoring normal wood chip stream flow to the mechanism after a limited predetermined time.
One objective of the apparatus disclosed in U.S. Pat. No. 5,263,651 is to provide a method or apparatus for treating wood chips which prevents damage to treating and destructuring apparatus due to the presence of tramp material. The invention disclosed in U.S. Pat. No. 5,263,651 operates in such a manner that when tramp material is detected, the chip flow is diverted from the chip processing apparatus. Good chips flow to the chip processing apparatus and chips with tramp material flow to a dumping bin. In this way, the flow of chips to the chip processing apparatus is interrupted when tramp material is detected, thus preventing damage to the destructuring apparatus due to the presence of tramp material. Essentially, the safety device of U.S. Pat. No. 5,263,651 operates as a separator. Importantly, because the safety device diverts the flow of chips when tramp material is detected, the fiber contained in the wood chips that are diverted from the processing equipment is lost.